The primary focus of these studies is the measurement of the synthesis and assembly of the endoplasmic reticulum (ER) during cell differentiation. The rates of synthesis of ER proteins will be measured in control and mitogen-tested murine splenic lymphocytes. These studies will help to determine the magnitudes of the increases in the synthesis of the ER proteins and whether there is a temporal order in the synthesis of these proteins. They are also intended to provide insights as to the relative contribution of transcriptional and translational control to the expression of the genes for the ER proteins. Another area of emphasis in this proposal is the membrane components involved in the processing of nascent proteins. Therefore, assays for signal peptidase, core glycosylation, and glycosyltransferases will be used to measure these processing functions in the ER from control and mitogen-treated lymphocytes. These studies will determine to what extent changes in these functions occur and in what order. They will also allow correlations to be made between the structure, composition, and processing activity of the endoplasmic reticulum.